This invention relates to two-way wireless communication using infrared radiation as a transmission medium. It may be used in electronic systems for interaction between computers, peripherals, and serial communication ports, where relatively short distance information exchanges are needed. The information is conveyed by infrared (IR) pulses. The primary interest is in serial IR (SIR) communication, but parallel IR is also feasible.
The use of infrared communications channels allows for short range, point-to-point data transfer and communications. Palmtop and laptop computers, in particular, will benefit from the ability to communicate without increasing system size, weight and, most importantly, power dissipation. Moreover, the use of wireless IR eliminates the need for bulky connectors. Wireless IR also has potential in many other applications, including information consumer apparatus, e.g., cellular phones, pagers and watches, remote unit data down-load, computer tablets, barcode readers, wireless LANs, data logging equipment, and more. Wireless IR has a potential application in any data transfer application where mechanical connector interface is impractical.
Recent developments have introduced such wireless communication systems, initially as a means of enhancing computer system portability. The infrared Data Association (IrDA) has pioneered standards for short-range, point-to-point communications. Narrow-field infrared is considered desirable for such communications. Each component in the communications network has a transmitter and a receiver.
The following relevant information is copied from an article in Electronic Engineering Times (Feb. 21, 1994):
The user model is a walk-up, point-to-point connection model. It involves making a conscious connection between the mobile and the fixed assets in the work environment, including desktop computers, printers, systemizers, modems, and, later, telephones. PA1 Depending on the system maker, the operating range varies between either 0 to 1 or 0 to 3 meters. The number zero is actually a system driver, because makers of the earliest systems using serial IR found that users, when they aren't getting the kind of response they want, tend to put the diodes right next to each other. This fact stresses the dynamic-range requirement in the analog portion of the receiver. The 1- or 3-meter numbers relate to what different company focus groups have found that users want. These groups have also found that a 30.degree. cone (the angular relationship between the transmitter and receiver) is sufficient for doing serial IR. PA1 IrDA members have already agreed on a number of key technical parameters. First, the maximum baud rate to be supported is 115.2 kbits/second. This is also the maximum baud rate for high speed PC serial ports. PA1 IrDA has decided to leave open the possibility of moving to 1 Mbit/s in the future. Such a jump requires a change in the wavelength of IrDA-compliant devices to 880 nm from 950 nm used in existing devices. Yet, most 880-nm devices still will be able to converse with 950-nm devices. Beyond this, serial IR operates in half-duplex and assumes an asynchronous charter-based universal asynchronous receiver/transmitter (UART) interface. To minimize power, the transmitter time is either 3/16 of the bit rate, or 1.6 microseconds. PA1 In the hardware portion of the serial IR approach, the link data comes from a UART. The format transmitter takes this data and translates it to a 3/16 pulse that is 3/16 of the bit time, or 1.6 microseconds. In other words, the format transmitter limits the duty cycle on the light pulse via the interaction of the shift register and the flip/flop. Specifically, the shift register outputs 1/16 the data and the flip/flop runs it out to 3/16 before closing off. Following this step, a GaAlAs LED translates the "data" current into "data" photons. PA1 On the receiving side, a lensed photodiode detector receives the "data" photons from the transmitter and translates it back into "data" current. The recovered current is amplified, digitized, and input to a format decoder to stretch the data back to the full bit time. PA1 Key trade-offs concern range vs. power, and power consumption vs. battery life, especially if the system needs a sleep mode. Accomplishing any of these allows increased receiver sensitivity and reduced transmitter power. The move to 3 meters alone requires a tenfold increase in power if the receiver system sensitivity does not increase. The best solutions will need to be able to take advantage, where possible, of low-power operation, especially because many PDAs are planning to operate on AA or AAA batteries. PA1 Regardless of the implementation, one issue is clear: The complete hardware system must be inexpensive. Many systems makers have already indicated their target cost for all elements of a system is less than $5. PA1 (1) A wide dynamic range is necessary because of the variations in distance between transmitter and receiver. PA1 (2) High speed signal transmission is required, and delays within and between transmissions must be minimized. PA1 (3) The intention to use batteries calls for significant conservation of power.
The foregoing quotation identifies several problems in providing a satisfactory wireless IR system:
Experience has shown that it is very difficult to provide a receiver which satisfies the desires of potential users, as outlined in the quoted material. In fact, it appears that no satisfactorily workable SIR receiver has been developed prior to the present invention.